The present invention relates to turbomachines, such as blowers, compressors, pumps and fans of the axial, semi-axial and radial type. The working medium or fluid may be gaseous or liquid.
The turbomachine according to the present invention may comprise one or several stages of which each usually includes one rotor and one stator; in individual cases the stage is formed by a rotor only.
More particularly, this invention relates to a turbomachine with at least one rotor, with the rotor comprising several rotor blades attached to a rotating shaft. At least one stator can exist, with the statar being provided with stationary stator blades. A casing exists which confines the passage of fluid though the rotor and the stator in the outward direction.
The aerodymamic loadability and the efficiency of turbomachines, such as blowers, compressors, pumps and fans, is limited by the growth and the separation of boundary layer on the blades as well as on the hub and casing walls. The state of the art proposes continuous boundary layer removal or continuous fluid supply for energization of the boundary layers as a measure against this fundamental problem. while the existing concepts can be quite effective with regard to the influence on the boundary layers obtained, the necessary secondary fluid mass flows are so large that the efficiency of the overall system in which they are applied can possibly be affected.
With regard to fluid removal, different methods are proposed which provide for removal of the boundary layer on the blade suction side via slots or holes or also fine-pore surfaces. Normally, the boundary layer is first led inside the blade and then removed from the respective blade and the main flow path of the turbomachine. Only one solution for a rotor provides for withdrawal of the boundary layer on the blade suction side and direct re-flow at the blade tip of the same blade. In addition, drafts exist which provide for circumferential slots on hub or casing before or behind a blade row to withdraw the sidewall boundary layer there. However, even if limited to parts of the operating range of the machine in specific cases, the influence on the boundary layers by fluid removal is always a continuous one.
The state of the art with regard to influencing boundary layers by fluid removal, in its substance, is summarized in the following documents:
1.) Withdrawal on the blade surface via holes, individual slots or porous zones                U.S. Pat. No. 2,720,356        U.S. Pat. No. 3,694,102        U.S. Pat. No. 3,993,414        U.S. Pat. No. 5,904,470        U.S. Pat. No. 5,480,284        
2.) Withdrawal on hub or casing via circumferential slots before/behind the blade row                Schuler et al.: Design, Analysis, Fabrication and Test of an Aspirated Fan Stage, ASME Paper 2000-GT-618, and        Merchant et al.: Aerodynamic Design and Analysis of a High Pressure Ratio Aspirated Compressor Stage, ASME Paper 2000-GT-619.        
With regard to fluid supply, various concepts for turbine blades exist, but these are not applicable to turbomachines since they essentially serve for surface cooling, not for boundary layer energization. From compressor cascade experiments, concepts are known in which air is blown out from a pressurized chamber in the blade interior to the blade suction side to energize the two-dimensional profile boundary layer. Related alternative proposals provide for direct passage of the fluid from the blade pressure side to the blade suction side. In addition, a concept exists for rotors which provides for the supply of air at hub and casing via axially symmetric slots to influence the wall boundary layers there. Finally, publications of research organizations exist showing concepts in which rotors are blown from individual nozzles in the vicinity of the casing to favorably influence the radial gap flow there. However, even if limited to parts of the operating range of the machine in specific cases, the influence on the boundary layers by fluid supply is always a continuous one.
The state of the art with regard to influencing boundary layers by fluid supply, in its substance, is summarized in the following documents:                U.S. Pat. No. 5,690,473        U.S. Pat. No. 6,334,753        U.S. Pat. No. 2,870,957        U.S. Pat. No. 2,933,238        U.S. Pat. No. 5,480,284        
Finally, concepts exist which provide for recirculation by way of fluid removal and fluid supply:                U.S. Pat. No. 2,749,027        
While the existing solutions may well be capable of exerting a positive influence on the flow, the disadvantage of the state of the art lies in the fact that the secondary fluid mass flows required must be so large that the efficiency of the entire installation, which may be established by the turbomachine with its secondary fluid system or also by a gas turbine, a jet engine, power station or another higher-level system, can possibly be impaired. Existing concepts employ neither the sources existing within the turbomachine nor those additionally provided outside of the turbomachine to effect pulsation or alternation of the secondary fluid flow, which would permit the boundary layers on the blade and wall surfaces of the main flow path of the turbomachine to be influenced with significantly smaller auxiliary mass flows.